I think the simple answer is that a long period seismometer will record both
local and long distance quakes, while a short period one will only record
local quakes. Some people with long period devices do filter off the high
frequency/short period signals to avoid picking up local human activity.
That would appear to make them less desirable for local quakes, when really
they are capable of sensing them quite well.
The "period" of the seismometer is a measure of the low frequency cutoff
point, or the longest period that it can measure. If properly damped, the
seismometer can sense signals to much higher frequency/shorter wavelength,
up to the limit of the recording system.
My opinion, anyways.
Keith
From: psnlist-request@.............. [mailto:psnlist-request@...............
On Behalf Of Len Polucci
Sent: Friday, October 15, 2010 1:52 PM
To: psnlist@..............
Subject: Re: Period of seismic units
Great, Great question! Since I have no idea and have wondered in the
past..I'd love to see some answers!
_____
From: Thomas Dick
To: psnlist@..............
Sent: Fri, October 15, 2010 10:32:41 AM
Subject: Period of seismic units
I asked Larry about this and he wanted me to post it here. I think he was
trying to get rid of me. It probably shows how little I know and that I am
missing something. This question came out of the activity in the Guy area
which is about 500 miles west of me as well as the New Madrid system which
is closer. It seems the records are better on the 2-4 Hz units. Here was my
question;
> It is about this geophone vs lehman or other long period instruments. In
> California you have many local quakes. These quakes have frequencies
> higher than long distance quakes. What is the logic of (just/or popularity
of) long
> period instruments out there? What precipitated this trend? The 1-5 Hz
units should be better on local events -- which you have a lot.
There are many California quakes and there is the activity in Washington
State and Yellowstone but you never see local seismic detectors being posted
with periods of 1-4.5 Hz -- except possibly tchannel. Shouldn't these units
help differentiate human noises like quarry activity from smaller local
earthquake activity?
__________________________________________________________
Public Seismic Network Mailing List (PSNLIST)
To leave this list email PSNLIST-REQUEST@.............. with the body of the
message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.
I think the simple answer is that a long period =
seismometer will
record both local and long distance quakes, while a short period one =
will only record
local quakes. Some people with long period devices do filter off =
the high
frequency/short period signals to avoid picking up local human =
activity.
That would appear to make them less desirable for local quakes, when =
really
they are capable of sensing them quite well.
The “period” of the seismometer is a measure =
of the
low frequency cutoff point, or the longest period that it can =
measure. If
properly damped, the seismometer can sense signals to much higher
frequency/shorter wavelength, up to the limit of the recording =
system.
My opinion, anyways…
&nbs=
p; Keith
From:=
psnlist-request@.............. [mailto:psnlist-request@............... =
On
Behalf Of Len Polucci
Sent: Friday, October 15, 2010 1:52 PM
To: psnlist@..............
Subject: Re: Period of seismic units
Great, Great question! Since I have no idea and =
have
wondered in the past..I'd love to see some answers!
From:=
Thomas =
Dick
<dickthomas01@.............>
To: psnlist@..............
Sent: Fri, October 15, 2010 10:32:41 AM
Subject: Period of seismic units
I asked Larry about this and he wanted me to post it here. I think he =
was
trying to get rid of me. It probably shows how little I know and that I =
am
missing something. This question came out of the activity in the Guy =
area which
is about 500 miles west of me as well as the New Madrid system which is =
closer.
It seems the records are better on the 2-4 Hz units. Here was my =
question;
> It is about this geophone vs lehman or other long period =
instruments. In
> California you have many local quakes. These quakes have =
frequencies
> higher than long distance quakes. What is the logic of (just/or =
popularity
of) long
> period instruments out there? What precipitated this trend? The 1-5 =
Hz
units should be better on local events -- which you have a lot.
There are many California quakes and there is the activity in Washington =
State
and Yellowstone but you never see local seismic detectors being posted =
with
periods of 1-4.5 Hz -- except possibly tchannel. Shouldn't these =
units
help differentiate human noises like quarry activity from smaller local
earthquake activity?
__________________________________________________________
Public Seismic Network Mailing List (PSNLIST)
To leave this list email PSNLIST-REQUEST@SEISMICNET=
..COM
with the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more =
information.